Activation of filamentary material



Jan. 8, 1946. D 5 GUS-HN ErAL 2,392,318

ACTIVATION OF FILAMENTARY MATERIAL Filed April l5, 1943 INVENTOR .5'. Gaaf/Af /V. /fBEYH/vr NO 0 I rl ri ATTORNEY Patented Jan. 8, 1946 2,392,318 ACTIVATION oF mAMEN'rAnY MATERIAL Daniel S. Gustin,

Bryant, East Orange, N. J.,

Electric Corporation,

of Pennsylvania inghouse Pa., a corporation Bloomeld, and Nelson H.

assignors to West- East Pittsburgh,

Application April 15, 1943, Serial No. 483,098

12 Claims. (Cl. 14S-13.1)

This invention relates to electron-emitting devices such as radio tubes, X-ray tubes and the like, and more particularly to the activation of iilamentary material which forms the cathodes thereof.

The primary object of our invention, generally considered, is to accurately activate iilamentary material for the cathode of electron-emitting devices by an improved method avoiding the use of such material as benzol vapor which is uncertain and dangerous.

Another object of the invention is to activate thoriated filamentary material in 5;. atmosphere produced by -passing a non-explosive protective iiuid, such as forming gas, through a mixture of xylene and dehydrated mineral oil.

A further object of our invention is to activate filamentary material, when mounted as a cathode for an electron-emitting device, by performing such operation when the iilament lies horizontal rather than vertical, thereby making it possible to hold such material at a more uniform temperature, and consequently produce more uniform activation.

A still further object of our invention is an accurately carbonized thoriated lament, adapted for electron-emission purposes.

Other objects and advantages of the invention, relating to the particular arrangement and construction of the various parts, will become apparent as the description proceeds.

Referring to the drawing:

Fig. 1 is an elevational view of a mount for an electron discharge device.

Fig. 2 is an elevational view, partly diagrammatic, of apparatus for activating the filament of such a mount. I

Various methods have been devised for the purpose of converting the thorium oxide content of drawn thoriated tungsten filaments to metallic thorium, so that the filaments are more efcient electron emitters when used as cathodes in electrical discharge devices.

A common method heretofore employed uses benzol vapor for applying carbon to the iilament to effect a reduction of the thorium oxide or suboxide content to metallic thorium during a subsequent seasoning schedule. Such seasoning is for the purpose of causing the added carbon to eiect a reduction of the thorium oxide content of the iilament. When the temperature is raised, the liberated thorium is directed to the surface of the filament. l

It has been found that using an atmosphere of hydrogen which contains benzol vapor for the purpose oi. carbonizing thoriated tungsten laments, is uncertain and dangerous. The hydrogen may explode and frequently does, and the amount of benzol vapor in the hydrogen depends upon the rate of iiow of the latter and the physical construction of the container. nActual results obtained may vary from almost no carbide to too much on the lament.

In accordance with our invention, we bubble forming gas, which is a non-explosive mixture of hydrogen and nitrogen, protective against oxi- 1 dation, preferably containing from 8% to 12% of grade dehydrated hydrogen, through xylene lCHdCHa) 2] which has been diluted with preferably an equal quantity of vacuum pump oil. The latter is a high mineral oil.

The oil used was grade 2970-1 in accordance with the Westinghouse Electric 8: Manufacturing Company Purchasing Department Specification No. 2970-1, approved June 2, 1921, revised September 5, 1938. In accordance with this, the oil shows not more than .005% ash, the volatile oil and moisture present does not exceed .02%, the specific gravity at 15.6 C. is between .90 and .91, the viscosity (Saybolt) at 38 C. is between 275 and 325 sec., and at 99 C. is between 50 and 55 sec., the minimum ash point is at 199 C., the minimum iire point is lat 230 C., and the steam emulsion number is a maximum of 90 seconds. It will, however, be understood that other oils are undoubtedly suitable for the purpose, so that we do not wish to be limited to the exact oil or one having the exact properties of that used.

We thereby obtain an atmosphere which is particularly desirable for lament carbonization or activation purposes. Cracked or combusted gas, produced as by incompletely burning illuminating gas, and having a typical composition of about 69% N., 13% H., 5% Coz, 12% C0 and .7% CH4, may be used instead of forming gas, although the latter is preferred because it is less toxic.

The xylene, which is the source of the carbon for the process, has been used undiluted, the forming gas being bubbled therethrough. Such a procedure gave a black deposit of carbon on the iilament at the filament temperature used, that is, when the filament was raised to a white heat, or to between 1900 C. and 2200* C. Raising the treating temperature of the filament helped to get away from the trouble, but also speeded up the reaction, giving less uniformity, and making the lament softer so that it sagged to an undesirable extent due to its own weight. Therefore, we diluted the xylene with pump oil, thus lowering the vapor pressure of the former, naturallylower than benzol, to slow down the reaction. Such dilution permits us to saturate the forming gas from the xylene mixture, and thus obtain a uniform carbonizing constituent in the gas. A dilution of one part of xylene to one part 4of pump oil was found desirable, but the process worked equally as well up to ve parts oi -pump oil to one part of xylene. Preferred operating temperatures range from 60 to 80 F.

Referring now to the drawing in detail, the

' containing a mixture of The apparatus for activating the filament II, and others of -like construction, is shown in Fig. 2, wherein I8 represents a flask, or otherreceptacle, xylene and pump oil I9, preferably within the limits of one part xylene to one to five parts of pump oil. The oil is preferably a high-grade dehydrated mineral oil, such as commonly used for lubricating vacuum pumps.

The activating atmosphere is produced by passing forming gas or its equivalent from a supply into the ask I8 and bubbling it from tube 2| through the diluted xylene I9, from whence .it passes through pipe 22 containing glass wool 23 or other material which will remove droplets, and then on to the chamber 24 in which the lament II of the mount, as illustrated in Fig. l, is activated.

The lament mount is desirably held in place, as by a washer 25, which may be formed of asbestos or other suitable material, around the are tube I4 to seal the space between said tube and the horizontally extending neck 26 of the envelope 24, against the entrance of air into said envelope. While the carbonized gas is passed through the envelope 24, the filament I I is desirably raised to a white heat, that is, to a temperature between 1900 C. and 2200 C., for a set interval, as controlled by timer 21 in circuit with source of power 28, The lower the treating temperature of the lament, the longer the treating time required for the same degree of carbonization or activation. The temperature of the filament, which is connected to said source of power through ammeter 29 and timer 21, is controlled by rheostat 3|, so that the filament is subjected to just the right amount of activation prior to the current being cut-oil by the timer. The flow of activating atmosphere through the envelope 24 is controlled by valve (not shown) in the pipe or tube leading from the source of gas supply so that a suirlcient, but not excessive, stream of such activating gas is supplied to the filament during the activating process.

From the foregoing it will be seen that we have improved on the method of activating filaments for discharge devices by substituting a nonexplosive atmosphere, accurately controllable because the vapor pressure is such that saturation of the gas is effected, for an explosive and uncertain atmosphere, at the same time providing for horizontal rather than a vertical position during activation, as well as for the accurate control, not only of the activating temperature of the filament, but also the duration of such activation. By activating the filament after mounting, breakage due to handling after embrittlement by the activating or carbonization process is avoided.

Although a preferred embodiment of our invention has been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

We claim:

l. The method of carbonizing thoriated lilamentary material comprising bubbling gas lene and dehydrated mineral through xylene diluted with oil to desirably reduce its vapor pressure, and heating said material in the atmosphere so produced.

2. The method of carbonzing thoriated filamentary material comprising bubbling a nonexplosive gas, protective against y oxidation, through xylene sufficiently diluted with oil to give it a desired vapor pressure, and heating said material in the atmosphere so produced.

3. The method of carbonizing thoriated filamentary' material comprising bubbling gas through a mixture of xylene and mineral oil, and heating said material in the atmosphere so produced.

4. The method of carbonizing thoriated. lilamentary material comprising heating in forming gas saturated by contact with a. mixture of one part of xylene and from one ,to five parts of dehydrated mineral oil.

5. The method of carbonizing a thoriated filament comprising introducing said filament while mounted on a stem into a vessel, passing gas through xylene diluted with oi1 to desirably reduce its vapor pressure, and then through said vessel, and simultaneously heating said filament.

6. The method of carbonizing a thoriated filament comprising introducing said nlament while mounted on a stem into a vessel, bubbling a nontherein.

7. The method of carbonizing a thoriated Illament comprising enclosing said lament while mounted on a stem in a through a passing said gas through said vessel, and simultaneously heating said filament therein,

8. The method of carbonizing a thoriated filament comprising enclosing said filament; while mounted on a stem in a vessel, saturating forming gas by bubbling it throug a mixture of Xysaturated gas through said vessel, and simultaneoisly raising said lament therein to al white hea 9. The method of carbonizing a thoriated filament comprising enclosing said filament while ment therein to between 1900o C. and 2200 C.

l0. The method of carbonizing a thoriated :fil-

heating said filament therein to between 1900" C. and 2200 C. for a, predetermined accuratelycontrolled period of time.

DANIEL S. GUSTIN. NELSON H. BRYANT. 

